Date: Thu, 21 Feb 2013 14:23:31 +0000 From: Xen.org security team <security@....org> To: xen-announce@...ts.xen.org, xen-devel@...ts.xen.org, xen-users@...ts.xen.org, oss-security@...ts.openwall.com CC: Xen.org security team <security@....org> Subject: Xen Security Advisory 36 (CVE-2013-0153) - interrupt remap entries shared and old ones not cleared on AMD IOMMUs -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Xen Security Advisory CVE-2013-0153 / XSA-36 version 4 interrupt remap entries shared and old ones not cleared on AMD IOMMUs UPDATES IN VERSION 4 ==================== Updated patches, to deal with a boot time crash resulting from the earlier changes on systems with firmware broken in a way not previously accounted for. ISSUE DESCRIPTION ================= To avoid an erratum in early hardware, the Xen AMD IOMMU code by default chooses to use a single interrupt remapping table for the whole system. This sharing implies that any guest with a passed through PCI device that is bus mastering capable can inject interrupts into other guests, including domain 0. Furthermore, regardless of whether a shared interrupt remapping table is in use, old entries are not always cleared, providing opportunities (which accumulate over time) for guests to inject interrupts into other guests, again including domain 0. In a typical Xen system many devices are owned by domain 0 or driver domains, leaving them vulnerable to such an attack. Such a DoS is likely to have an impact on other guests running in the system. IMPACT ====== A malicious domain which is given access to a physical PCI device can mount a denial of service attack affecting the whole system. VULNERABLE SYSTEMS ================== Xen versions 3.3 onwards are vulnerable. Earlier Xen versions do not implement interrupt remapping, and hence do not support secure AMD-Vi PCI passthrough in any case. Only systems using AMD-Vi for PCI passthrough are vulnerable. Any domain which is given access to a PCI device can take advantage of this vulnerability. MITIGATION ========== This issue can be avoided by not assigning PCI devices to untrusted guests. In Xen versions 4.1.3 and above the sharing of the interrupt remapping table (and hence the more severe part of this problem) can be avoided by passing "iommu=amd-iommu-perdev-intremap" as a command line option to the hypervisor. This option is not fully functional on earlier hypervisors. RESOLUTION ========== Applying the appropriate attached patch resolves this issue. Note that on certain systems (SP5100 chipsets with erratum 28 present, or such with broken IVRS ACPI table) these patches will result in the IOMMU not being enabled anymore. This should be dealt with by a BIOS update, if available. Alternatively the check can be overridden by specifying "iommu=no-amd-iommu-perdev-intremap" on the Xen command line ("iommu=amd-iommu-global-intremap" on 4.1.x), at the price of re-opening the security hole addressed by these patches. xsa36-unstable.patch Xen unstable xsa36-4.2.patch Xen 4.2.x xsa36-4.1.patch Xen 4.1.x $ sha256sum xsa36*.patch 4bdc0f1f94f82c6bc6c777971f22ef915215b72b98b29f9064e4df65c0efc6f4 xsa36-4.1.patch dd32ecaa84edbf6d11241045f40ba53ec4a3bc6c24f719bc21204067c4eb8964 xsa36-4.2.patch 7c0b3a1b332a24a830c7a436b065943f60c54cd5b7e746c440e2992a7b5cfe41 xsa36-unstable.patch $ Incremental patches on top of what was provided in version 3 can also be taken from the respective mercurial trees: http://xenbits.xen.org/hg/xen-unstable.hg/rev/e68f14b9e739 http://xenbits.xen.org/hg/staging/xen-4.2-testing.hg/rev/6a03b38b9cd6 http://xenbits.xen.org/hg/staging/xen-4.1-testing.hg/rev/4d522221fa77 -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.10 (GNU/Linux) iQEcBAEBAgAGBQJRJf98AAoJEIP+FMlX6CvZ5ocH/jNY92kLw7BOencxa9R3TGTn 20O0+j1id+xi2vjVVF2xm2SJ7g/6Egx5WURUfy2cu+I8GdDHKmRrp3Vkazltzcnd 6AlI5aiPC2H1rFkU0FpneRk3mrluABLZO8Q5YcSJs24hwqded0W+SivH63aInki/ PsDGoBu8HUjYMWjXyqCJVJIGToLS9ApaQ8+iTylWb1ZocRm2VcPS8yJI7z82kj3A zRNADG36oAFawSJsE9z3ykVoYv9UYckOaWkaXh7jZPHAvIjvP2wLb9gmMkMXbIOP ICpJJFf0w7oW6KTY3g9n8CxUMBMoUw/9Fv+CQBzOf0ZZY/vIE8q65A0NhCcWixo= =vmpB -----END PGP SIGNATURE----- Download attachment "xsa36-4.1.patch" of type "application/octet-stream" (14403 bytes) Download attachment "xsa36-4.2.patch" of type "application/octet-stream" (12586 bytes) Download attachment "xsa36-unstable.patch" of type "application/octet-stream" (12528 bytes)
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